TROJ_DLOADER.YPS

April 06, 2013
 Analysis by: Anthony Joe Melgarejo
 ALIASES:

Trojan:Win32/Ircbrute (Microsoft), Trojan Horse (Symantec), W32/Dorkbot-EU (Sophos), Trojan.Win32.Ircbrute (Sunbelt), W32/Blocker.AZAY!tr (Fortinet), Trojan-Dropper.Win32.Injector (Ikarus), Win32/Injector.AERP trojan (ESET)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

272,384 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

05 Apr 2013

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following copies of itself into the affected system and executes them:

  • %Application Data%\{random file name}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It terminates the execution of the copy it initially executed and executes the copy it drops instead.

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name}.exe = "%Application Data%\{random file name}.exe"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name}.exe = "%Application Data%\{random file name}.exe"

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}le.com/dl/201433197/a76b191/co937ty78934uti.html
  • http://{BLOCKED}le.com/dl/201468511/672e785/374844578.html
  • http://s374.{BLOCKED}le.com/get/11f2eea923e1d880b13671034f49d8aae291acbe/515e8321/2/501befb7d8fad531/c022a5f/374844578
  • http://s612.{BLOCKED}le.com/get/ff0634635d66b2625429bdb650a3dcc0768c0ab7/515e831b/2/cbef13f353d1fb89/c01a06d/co937ty78934uti

It saves the files it downloads using the following names:

  • %User Temp%\{random file name 2}.exe
  • %User Temp%\{random file name 3}.exe

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • f.{BLOCKEDon.pl

It deletes the initially executed copy of itself